Living and non-living catalysts have been used to polymerize olefins. In a living polymerization, each catalyst molecule initiates a growing polymer chain that does not undergo chain transfer or termination reactions while monomer is present. By comparing the number of initiator molecules with the number of polymer chains produced in the final polymer, one can determine whether or not a living polymerization has occurred. These two numbers should be equivalent to be a true living polymerization. If there are a substantially greater number of chains, then the polymerization is not living.
Titanium tetrachloride (TiCl.sub.4), boron trichloride (BCl.sub.3), tin tertachloride(SnCl.sub.4), iron trichloride (FeCl.sub.3), aluminum trichloride (AlCl.sub.3) systems and the like have been described in U.S. Pat. Nos. 4,910,321 and 4,929,683, and European patent application 341,012 for use in the living polymerization of olefins. The basic components of these systems include a Lewis acid, a tertiary alkyl initiator molecule containing a halogen, ester, ether, acid or alcohol group and an electron donor molecule such as ethyl acetate. The exact combination of the elements varies with each system. The tertiary alkyl initiators used in these systems are used for living and non-living carbocationic catalysts. The tertiary alkyl initiators are typically represented by the formula: ##STR1## Wherein R.sub.1, R.sub.2, and R.sub.3 are a variety of alkyl or aromatic groups or combinations thereof, n is the number of initiator molecules and X is the functional group on which the lewis acid affects a change to bring about the carbocationic initiating site. This group is typically a halogen, ester, ether, alcohol or acid group depending on the lewis acid employed. One or two functional groups per initiator tend to lead to linear polymers while three or more tend to lead to star polymers.
As discussed in U.S. Pat. No. 5,169,914, the chosen electron pair donor component of the above systems directly relates to the ability of these catalysts to stabilize the carbocation formed and to generate living conditions. Electron pair donors have been defined as molecules capable of donating electron density to an electron deficient site. These molecules usually contain heteroatoms and heteroatomic functional groups including amides, ester, ethers, sulfoxides and the like. The electron donor number concept has been used to explain the activity of early catalyst systems which employ ether and ester initiators. It was believed that the formation of in situ electron pair donors were responsible for the catalyst characteristics. However, the role of the electron donor is still uncertain and has been challenged. See M Gyor, L. Balogh, H. C. Wang, R. Faust, Polym. Prepr. Amer. Chem. Soc. 33 (1), 158(1992).
Catalyst systems based on boron trichloride and titanium tetrachloride using various combinations of the above components typically have similar process characteristics. First, Lewis acid concentrations must exceed the concentration of initiator sites by 16 to 40 times in order to achieve 100 percent conversion in 30 minutes (based upon a degree of polymerization equal to 890) at -75 to -80 degrees C. These catalyst systems are also typically used with solvents. For example, the references above disclose methyl chloride as a preferred solvent and that a mixed solvent may be used to avoid side reactions or to keep the polymer in solution. Further the mixed solvent should provide some degree of polarity to maintain the polymerization rate. However, even in these circumstances, an electron pair donor must be present.
For an industrially applicable process these catalysts and polymerization conditions fall short of commercial usefulness. Improvements in these systems would include elimination of boron and titanium based lewis acids as they present handling and purification problems. Also a reduction in the amount of catalyst used would be preferred and a reduction in polymerization time would be preferred.